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Dan D'agostino Relentless Preamplifier

The Relentless Preamplifier 


The new Relentless Preamplifier is the ultimate in preamplifier design. The preamplifier plays a critical role in musical playback; the point in the reproduction stage when the music signal is particularly susceptible to compromise through noise and distortion. The use of three separate chassis in the design of the Relentless Preamplifier—a dedicated audio chassis for each channel separated by a power supply/control section—addresses these challenges and brings other benefits as well.


Power Supply  


Positioned between the two audio channels, the power supply makes use of extensive electrical and magnetic shielding to keep radiated interference out of critical preamplifier circuits. Internal line conditioning circuitry filters RF noise on the AC power and compensates for asymmetric power waveforms and DC on the mains. Power for the preamplifier stages comes from two 150 VA toroidal transformers – one dedicated to the analog circuitry and one for the digital and control circuitry. These transformers drive an 8-amp bridge rectifier and 26,400 microfarads of filter capacitance. The two regulators for the analog stages are scaled-down versions of those used in the Relentless Mono amplifier. The separate digital regulator is a monolithic platform with thermal and current limiting protection in the unlikely event of a fault. The Relentless Preamplifier has nearly as much power supply capability as many power amplifiers.


Room to Breathe 


The input stage in each mono preamplifier is the result of a design experiment for a circuit that hadn’t been used in any previous D’Agostino preamplifier. As part of development, a version was tested in the existing Momentum Preamplifier. The overwhelmingly positive results led directly to the launch of the Momentum HD Preamplifier. From there, the fullest expression of this idea was developed, and the Relentless Preamplifier was underway.


The audio circuit topology starts with a new discrete differential FET input stage featuring a voltage input signal capability of an extraordinary 30 volts. With an input impedance of over 1 MOhm, the Relentless Preamplifier’s front end is immune to source related electrical issues. In normal operation, component heating can lead to performance and sonic degradation. Developed specifically for the Relentless Preamplifier, a unique circuit maintains a stable bias so that temperature related anomalies are offset thus preserving performance during extended listening.


Featuring only balanced XLR inputs the Relentless Preamplifier topology rejects common-mode input noise over an unusually wide bandwidth. All signal gain is realized in the current domain using proprietary multiple-output current mirrors with nearly 30 times the linearity of other designs. Executed with four-layer circuit boards for superior signal quality. The use of four-layer boards dramatically reduces distortion and propagation levels as compared to the more commonplace, two layer boards.


The analog and digital circuit elements are isolated, including ground planes, from each other. Where necessary, digital control signals are optically coupled to analog circuits. The signal switching relays are hermetically sealed and use gold-plated contacts for maximum signal integrity.


Utilizing no negative feedback anywhere, core D’Agostino circuit concepts include a signal path that is fully complementary and balanced from input to output achieving a frequency response flat to 120 kHz.. The overall result is a musically dense and dynamically rich signal presented to the balanced outputs.


Separate but Linked 


Arguably, the most striking element of the Relentless Preamplifier is the pair of volume controls fronting the two audio chassis. Volume control circuits are often overlooked, if not actively minimized, in preamplifier designs. This is not the case in the Relentless Preamplifier. Each volume control is constructed using 14 separate metal components ensuring the smoothest response and control of the military-grade, high-linearity solid-state switches and discrete precision resistors employed in the volume circuit. The bandwidth and transient response of the Relentless Preamplifier is completely unaffected by the volume setting. As a result, high frequencies sound especially smooth and extended, and music emerges from “jet black” silence.


The volume settings are displayed via the elegant swiss watch inspired volume wands or can be displayed numerically, from 0 to 99.


Frequency Response


0.1 Hz to 120 kHz, +/- 0.0 dB

Signal-to-Noise Ratio


-105 dB, unweighted / -100 dB, weighted



+ 8/+14dB selectable



Silver or Black with Custom Finishes Available Upon Request

Total Harmonic Distortion


<.006%, 20Hz to 20kHz



5 pr - Balanced via XLR connectors



2 pr Balanced via XLR connector for Zone 1, 1 pr Balanced via XLR



17 x 1.75 x 17 in / 43.2 x 34.9 x 43.2 cm



132 lb / 60 kg



Relentless_Preamp_Manual.pdf (9.82 MB)

Dimensions (Preamp)


17x 3.9 x 17 in / 43.2 x 9.9 x 43.2 cm

Dimensions (Power Supply/Base)


17 x 3.9 x 17 in / 43.2 x 9.9 x 43.2 cm

Analog Inputs


5 stereo pairs of balanced XLR

Digital Inputs (w/DAC Module Installed)


1 USB A type, 1 Optical, 1 SPDIF, 1 coaxial, Ethernet RJ45, 1 WiFI




Dan D'agostino Relentless Preamplifier

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